Reflex sights for weapons are well known in the art. Such sights use an image of a reticle reflected from a semi-transparent mirror surface, through which mirror the shooter views the target. Optics cause the reticle image to appear at or near infinity, parallax free, and in focus with the target. The optics may be a refracting lens in the system that collimates the reticle image. The mirror surface may be concave so that it collimates the reticle image as it reflects it. The sight magnification is 1× unity.
“Heads-Up Display” (HUD) reflex sights are known for use on weapons. The HUD or reflex sight is made up of an optical collimating reflector, mechanical adjustments and packaging, and an electronic light source. Conventional optical methods for collimating and reflecting the aimpoint to the eye use very basic classical optics. Generally, the reflex sights are one or two element off-axis reflectors with cover windows to zero the optical power of the scene (near unity 1× magnification) and/or provide environmental seals. The optical power of the see-through scene is normally non-adjustable. The optics may be able to change the virtual image of the reticle (i.e., the focal distance) in order to place the image at infinity or any other desired distance.
To combine the aimpoint wavefront with the scene, the typical reflex sight uses a partially mirrored coating or, for more efficiency, a multilayer dielectric dichroic coating, which reflects a narrow wave length of the reticle's image color (e.g., a red or green aimpoint) and transmits the visible spectrum of the scene. The hologram relies on diffraction to bring the colored aimpoint into the scene. Such reflex sights are mentioned in U.S. Pat. No. 5,901,452 to Clarkson, the disclosure of which is incorporated herein by reference.